Even John Lewis warns of a new year hangover

Barnstorming online sales helped John Lewis post strong festive trading, although it has warned of a sharp drop in its performance since Christmas Day and a "challenging" year ahead for the sector.

The retailer, which has 29 department stores and six John Lewis at Home shops, posted a 6.2% rise in underlying sales for the five weeks to 31 December.

John Lewis's sales performance is likely to be ahead of many of its high street rivals during a brutal consumer downturn.

Boosted by three new stores and a 27.9% surge in online revenues, John Lewis delivered a 9.3% jump in total sales to £596 million over the five-week period. Its online sales smashed through the £600 million barrier in December for the year to date.

Andy Street, managing director of John Lewis, which with Waitrose forms the John Lewis Partnership, said: "Sales during the four weeks to Christmas Eve were outstanding." But John Lewis's total sales fell by 4.8% between 25 December and New Year's Eve.

The retailer blamed the fall on being up against strong comparable sales for the same week last year, when consumers splashed out on big-ticket items ahead of the VAT rise to 20% in January 2011. Street warned "trade in 2012 will undoubtedly be challenging and economic conditions volatile".

The operating profit collapsed by 54.5% to £15.8 million for the six months to 30 July, as its "never knowingly undersold" policy, which matches the prices of branded goods sold by its rivals, took its toll at a time of intense discounting on the high street.